Corrosion inhibited poly(hexafluoropropylene oxide) oil compositions



United States Patent Ofiice 3,306,854 Patented Feb. 28, 1967 CORROSION INHIBITED POLY(HEXAFLUORO- PROPYLENE OXIDE) OIL COMPOSITIONS William H. Gumprecht, Wilmington, DeL, assignor to E. 1. du Pont de Nemours and Company, Wilmington,

Del, a corporation of Delaware No Drawing. Filed Mar. 24, 1966, Ser. No. 536,969 7 Claims. (Cl. 25249.9)

in which R is a perfluoroalkyl group having 1 to about 6 carbon atoms. These oils may be tailored, if desired, to operate at temperatures as high as 800 F. They are not affected by either oxygen or moisture at these temperatures.

At operating temperatures up to about 400 F., these oils have no apparent adverse eliect on metals. However, when operating at temperatures of 500 to 700 F., corrosion has been found to occur especially with metals such as steels, stainless steels, magnesium, aluminum, silver, titanium, copper and bronze. Accordingly, it is desirable to provide corrosion inhibitors which prevent corrosion of metals in contact with these oils at extreme temperatures.

To be useful in this situation, a corrosion inhibitor must possess a number of specific properties. First of all, it must inhibit corrosion. Furthermore, it must be soluble in and compatible with the oil. The solubility must be suflicient to provide an effective amount of inhibitor in the oil, both at operating temperatures and at ambient temperatures. There must be no separation of the inhibitor from the oil even while the device containing the oil is not in use. The inhibitor itself must also possess a high degree of thermal stability at the temperatures at which the oils are used. An inhibitor which decomposes under operating conditions will lose its effectiveness rapidly. Moreover, the inhibitor should not seriously affect lubricant properties, particularly lubricity, oilviscosity and oil viscosity index. These and other requirements eliminate most, if not all, known corrosion inhibitors.

It is an object of this invention to provide poly(hexafluoropropylene oxide) oil compositions containing corrosion inhibitors which considerably reduce or prevent corrosion of metals even at extremely high temperatures. Other objects will become apparent from the following description of this invention.

It has now been discovered that reduced corrosion of metals in the presence of poly(hexafluoropropylene oxide) oils can be obtained by using a poly(hexafiuoropropylene oxide) oil composition which comprises poly(hexafluoropropylene oxide) oil of the structure where n, p and r are integers indicating the degree of polymerization and Rf is a perfiuoroalkyl group having 1 to about 6 carbon atoms, said oil having an average molecular weight of at least about 3,000 and a pour point not in excess of about 50 F. and, as corrosion inhibitor, an effective amount of cyclic phosphonitrilate ester of the structure where X is R O{CF(CF )CF O} CF(CF )CH O in which in is 0 to about 12 and R is as previously stated.

Poly(hexafluoropropylene oxide) oils of the above structures are extremely stable to elevated temperatures. Those polymers having average molecular weights of at least about 3,000 and pour points not in excess of about 50 F. are quite useful as lubricating oils. Polymers of the type having an average molecular weight of about 5,500 to 7,000 are preferred. These molecular weight designations are based upon number average molecular Weights obtained by the spectroscopic method. The pour point designation is based upon Federal Test Method Standard 791, method 351.

These poly(hexafluoropropylene oxide) oils may be prepared in several ways. Hexafiuoropropylene oxide is readily homopolymerized to products of the structure CF CF CF O{CF (CF CF O} CF (CF COF Where n is 0 or an integer indicating the degree of polymerization, as described in Canadian Patent No. 725,740, issued January 11, 1966. Polymers of the structure where x and y are each 1 to about 4, are prepared by polymerizing hexafluoropropylene oxide in the presence of a ketone of the structure as described in Canadian Patent No. 707,363, issued April 6, 1965. Polymers of the structure where z is 0 to 1 are prepared by polymerizing hexafluoropropylene oxide in the presence of an acid fluoride of the formula F(CF COF as described in French Patent No. 1,362,548.

All of the above polymers are readily hydrolized in the presence of water to the corresponding acids of the structure R O{CF(CF )CF O},,CF(CF )COOI-I where R, is a perfiuoroalkyl group having 1 to about 6 al carbon atoms. The acids derived from these products react with elemental fluorine according to the method of- British Patent No. 1,000,802 to form R O [CF CF CF CF CE; CH OH These polymers also dimerize under the influence of ultraviolet light, as described in U.S. Patent No. 3,214,478, to form oils of the structure The cyclic phosphonitrilate esters used as corrosion inhibitors in the compositions of this invention can be prepared by reaction of a cyclic phosphonitrilic dihalide of the formula (NPCl where a is 3 or 4, With an alcohol of the structure a orcmcrncr o-i cr cr,

as described in US. Patent No. 3,201,445 to Drysdale, Fassnacht and Le Bleu. by reduction of the corresponding acid fluorides of the structure R O[CF(CF )CF O] CF(CF )COF, as described by Le Bleu and Fassnacht in US. application Serial No. 287,777, filed June 14, 1963. These cyclic phosphonitrilate esters are only slightly volatile and are useful lubricants in their own right. For inhibition of high temperature corrosion, the preferred inhibitors are the cyclic phosphonitrilate esters of the structure The poly(hexafluoropropylene oxide) oil composition should contain an effective amount of cyclic phosphoni trilate ester as corrosion inhibitor. By effective amount is meant the amount required to produce a useful inhibitor effect for the required service life of the device containing the oil at the operating temperature. Various metals dififer considerably in the amount of corrosion which will occur and the amount of inhibitor required to prevent high temperature corrosion. Furthermore, inhibitor is probably consumed while doing its job, hence increased service life or higher use temperatures will require larger amounts of inhibitor.

In general, the amount of cyclic phosphonitrilate ester in the oil composition will be in the range of about 0.1 to 2% by Weight. So long as at least about 0.1% of inhibitor is present, a significant amount of corrosion inhibition is obtained. As the amount of inhibitor is increased, a quantitative reduction in corrosion is obtained up to a point. At about 1% by weight concentration the effect reaches a maximum; higher concentrations seldom producing any significant increase in effect. For a general purpose high temperature oil, it is usually preferable to add about 0. 5 to 1.5% by weight of inhibitor. This amount is suflicient to meet the requirement of the vast majority of needs for the oils.

The following examples, illustrating the novel oil compositions of this invention and their utility, are given without any intention that the invention be limited thereto. All percentages are by weight.

Examples 1 to 8 The compositions of this invention are tested using a modified form of the apparatus specified in the WADD Microoxidation-Corrosion Test of High Temperature Fluids, Fluids and Greases Section, Aeronautical Systems Division, Wright-Patterson Air Force Base, replacing the specified Pyrex tube with an Inconel tube. Basically the apparatus consists of a /s in. nickel tube adapted for mounting three washers outside the lower end. The Ms in. tube is inserted inside a in. vertical nickel tube so that the washers are immersed in a body of oil contained in the larger tube. The larger tube, which is adapted with a condenser for recovering any oil which may be stripped from the tube, is inserted in an aluminum heating block.

These alcohols can be prepared Various steel washers having the following compositions are used:

. 18% Cr, 8% Ni, 2% Mn, 1% Si, balance Fe.

18% Cr, 14% Ni, 3% Mo, 2% Mn, 1% Si, balance Fe.

The test consists of placing test washers of the metals to be tested in the apparatus, adding suflicient oil composition to insure the washers are covered, assembling the remaining apparatus and inserting it in the heating block. The fluid is then heated to the test temperature and air is passed down through the smaller nickel tube into the body of oil containing the washers. Test temperatures of 650 and 700 F. are used.

Corrosion is determined by weighing the test washers before and after the test. The corrosion rate is calculated from the weight change and the known surface area of the washer. Before weighing, both before and after the test, the test Washers are metallurgically cleaned, i.e. scrubbed with securing powder and water, rinsed with water, degreased and dried with acetone.

Two different oils are used in these examples. Oil A is a hexafluoropropylene oxide polymer of the structure having an average molecular weight of 6,200. Oil B is a hexafluoropropylene oxide polymer of the same structure which has been heat treated to remove less stable components. It has an average molecular weight of 6,100. The inhibited oil compositions contain 1% of a cyclic phosphonitrilate ester of the structure For comparison, control experiments in which no inhibitor is added to the polymer oil are carried out for each example.

The following table summarizes the test conditions and results for these examples.

TABLE II Weight change, mgJcrnfl/day Example Oil Temp., Metal Control With Inhibitor A 650 2. 24 l. 60 A (350 1. 53 0.95 A (350 301 Stainless -0. 81 0. 05 A 650 Titanium (8% Mn) 1. 35 1. 09 A 650 Silver 0. 28 0. 23 A 700 (DQ454536 Steel 2. 15 0. (56 B 700 301 Stainless..- 0. 76 0. 48 A 700 316 Stainless 1.95 0. 006

Examples 9 to 15 When Examples 1 to 6 and 8 above are repeated using 011 C, a poly(hexafluoropropylene oxide) oil of the structure n-C H OCF (CF CF O5 CF CF having an average molecular weight of 6,000, results essentially identical with those shown for Oil A in Table II above are obtained.

Examples 16 to 23 When Examples 1 to 8 above are repeated using a cyclic phosphonitrilate ester of the structure [CF CF CF O{CF(CF CF O} CF(CF CH O] (PN 3 in place of the cyclic phosphonitrilate ester used above,

decreases in corrosion of the same order of magnitude as those shown in Table II above are obtained.

Although the invention has been described and exemplified by way of specific embodiments, it is to be understood that it is not limited thereto. As will be apparent to those skilled in the art, numerous modifications and variations of these embodiments may be made without departing from the spirit of the invention or the scope of the following claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. A poly(hexafluoropropylene oxide) oil composition which comprises a major amount of base oil selected from the group consisting of poly(hexafluoropropylene oxide) oils of the structure Where n, p and r are integers indicating the degree of polymerization and R is a perfluoroalkyl group having 1 to 6 carbon atoms, said oil having an average molecular weight of at least 3,000 and a pour point not in excess of 50 F. and an effective amount of corrosion inhibitor selected from the group consisting of cyclic phosphonitrilate esters of the structure and where X is RgO'ECF (CF cF ol CF (CF CHzO- in which m is 0 to 12 and R: is as previously stated.

2. The composition of claim 1 in which the poly(hexafluoropropylene oxide) oil is of the structure and 0.1 to 2% by weight of cyclic phosphonitrilate ester of the structure the poly(hexafluoropropylene oxide) oil has an average molecular weight of 5,500 to 7,000 and 0.5 to 1.5% of cyclic phosphonitrilate ester is present.

4. The composition of claim 3 in which in is 4.

5. The composition of claim 1 in which the poly(hexafiuoropropylene oxide) oil is of the formula and 0.1 to 2% by weight of cyclic phosphonitrilate ester of the structure is present.

6. The composition of claim 5 in which R is CF CF CF the poly(hexafiuoropropylene oxide) oil has an average molecular weight of 5,500 to 7,000 and 0.5 to 1.5% of cyclic phosphonitrilate ester is present.

7. The composition of claim 6 in which m is 4.

References Cited by the Examiner UNITED STATES PATENTS 2,876,247 3/1959 Ratz et al. 25249.9 X 2,876,248 3/1959 Ratz et al. 25249.9 X 3,201,445 8/1965 Drysdale et al. 25249.9 X 3,214,478 10/1965 Milian 260-615 DANIEL E. WYMAN, Primary Examiner.

W. H. CANNON, Assistant Examiner. 

1. A POLY(HEXAFLUOROPROPYLENE OXIDE) OIL COMPOSITION WHICH COMPRISES A MAJOR AMOUNT OF BASE OIL SELECTED FROM THE GROUP CONSISTING OF POLY(HEXAFLUOROPROPYLENE OXIDE) OILS OF THE STRUCTURE 